1. Technical Field
A “Flexible Mobile Display” provides a thin flexible display for mobile phones or other handheld or portable computing devices that is foldable and/or rollable without damaging optical characteristics of the flexible display in order to provide a large display in a compact user extensible form factor.
2. Related Art
One of the biggest complaints with today's mobile phones or other handheld or portable computing devices is the limited display size. Foldable displays have been suggested as one possible solution to this complaint. However, many proposed or prototype foldable display solutions may be impractical as the mechanical stress along folds may be too extreme to allow reliable operation over many folding cycles. Suggestions for rollable displays also have raised a number of potential problems. For example, most proposals for rollable displays use an active matrix in order to provide video capability. An active matrix, unfortunately, presents serious material issues for rollable displays as the transistors tend to fail under the repeated bending caused by rolling the displays.
In general, rollable displays can divided into emissive and reflective types. OLED is the main emissive type proposed. OLED has a number of problems. One of the most serious problems is that OLED cannot tolerate water vapor and require stringent hermetic sealing. For rollable OLED displays, this becomes a very difficult material issue to solve. OLED also has relatively low light emission efficiency when compared to inorganic LEDs. Combining with the fact that OLED is a Lambertian light emitter and do not have directional gain, rollable OLED displays will consume significant amounts of power, thereby limiting their utility for portable devices. Reflective rollable displays in general have lower hermetic sealing requirements than OLED and may be closer to reality than the OLED ones. The manufacturability and durability issues, however, remain, especially given the fact that almost all of them require active matrix driving. Also, for most of them, video rate operation and good color rendition remain unsolved issues.
As an alternative to active matrix type displays, there are a several passive matrix displays that can potentially be rollable, but suffer other problems. For example, one recent technology, which can be viewed as an electrophoretic display with an air medium, uses electret particles, particles with semi-permanent electric charges, and can achieve video rate for smaller matrices. This technology suffers from limited reflectivity, especially in color mode, restricted color gamut, and potential durability issues. Further, electret particles may suffer from charge loss from impacts with the electrodes. In addition, humidity changes have been known to affect the threshold voltage needed for proper passive matrix operation.
Another type of passive matrix display referred to as MEMS is bistable and offers limited gray scale capability. However, the color gamut is relatively small. Unfortunately, the technology of such displays is relatively immature and currently even manufacturing of a rigid version is still in the planning stages. As such while MEMS type displays may provide viable solutions in the future, no such displays in foldable or rollable formats are currently commercially available.